1. Field of the Invention
The present invention relates to a liquid storage tank trailer. More particularly, the present invention relates to an improved mobile liquid storage tank trailer with enhanced safety features.
2. Description of the Related Art
A number of different types of fluid storage tank trailers exist which can be towed from one location to another. Two such tank trailers are described in U.S. Pat. Nos. Des. 253,051, and 4,874,184. These fluid storage tanks are generally trapezoidally-shaped from the forward end to the rear end enabling them to be supported at the rear end upon a pair of ground engaging wheels at a time when the fluid storage tank has its front end lifted upwardly, and secured behind a towing vehicle so that the top of the tank becomes substantially horizontal.
The trapezoidally-shaped fluid storage tanks of U.S. Pat. Nos. Des. 253,051 and 4,874,184 are constructed such that when the tank is resting upon the ground, the tank top slopes gradually downward. A problem with this type of construction, however, is that when a person is standing on the top of the tank for purposes of filling, cleaning and performing other operating and maintenance procedures, the sloped top of the tank presents a substantial risk of slipping and falling to that person. This is particularly true in inclement weather conditions where the top of the tank has become iced or is extremely slick.
Solutions to this problem have been attempted in the past in which stepped tops have been provided. For example, U.S. Pat. No. 5,004,269 describes a fluid storage tank having a top comprised of a multitude of discrete steps which gradually slope downward from the rear to the front of the tank, when the tank is unhooked from a towing vehicle and resting on the ground. Similarly, U.S. Pat. No. 5,213,367 also describes a fluid storage tank that has a top comprised of a single discrete step.
Unfortunately, both of these construction designs create additional problems. One such problem is the cost of constructing these tanks. Tanks having a sloped surface, though quite dangerous to walk on, are much cheaper to build than multi-stepped tanks since they are constructed of a single piece of sloping material. On the other hand, the multi-step tank design in which the steps extend from one side of the tank to the other is much more complicated, costly and time-consuming to build as each riser piece and step plate must be individually constructed and then fit together.
In addition to the additional construction cost, both the multiple step top tank of U.S. Pat. No. 5,004,269 and the single, bi-level top tank of U.S. Pat. No. 5,213,367 require vertical ladders for a person to access the top. Such vertical ladders present a significant safety hazard, particularly in inclement weather where the vertical ladders may become slick or slippery.
Thus, both safety and economics have driven the need for a mobile fluid storage tank having a roof top that is not dangerous to workers walking thereon, that does not require a vertical ladder for access, and yet is relatively simple to construct.